The present invention relates to an optical wireless communications system for transmitting, for example, video signals to a video system in which a video supply apparatus and a video display apparatus are separated from each other.
Illustrated in FIG. 1 is a known separated-type video system in which a video supply apparatus 1 and a video display apparatus 2 are separated from each other. Video and audio signals are transmitted from the video supply apparatus 1 to the video display apparatus 2 through a dedicated connector cable 3.
When users purchase separated-type video systems such as home-use plasma display TVs, an about 3 m-length connector cable is attached to each TV as an accessory. Thus, he or she must purchase another longer connector cable, if required. Such a connector cable is elastic and usually has a diameter of about 10 mm. Thus, care must be taken when laying a connector cable.
A thin video display apparatus of a known separated-type video system can be hung over a wall but requires a relatively thick connector cable laid on the wall, which marring the beauty. Moreover, the location of placement of a video supply apparatus, such as a tuner, is limited due to the connector cable laid on the wall. Therefore, the video supply apparatus and the video display apparatus cannot be freely placed apart from each other.
A known electromagnetic video/audio transmission interface instead of such a connector cable has a limited transfer speed and requires signal compression.
Also illustrated in FIG. 2 is a known optical wireless communications system disclosed, for example, in Japanese Unexamined Patent Publication No. 2000-22632.
This system is equipped with an optical transmitter 4 set on a video supply apparatus 1 and an optical receiver 5 set on a video display apparatus 2. The optical transmitter 4 emits an optical signal modulated with video and audio signals. The optical receiver 5 receives and demodulates the optical signal to reproduce the video and audio signals. A laser diode used as a photoemitter for the optical transmitter 4 serves to transmit an optical signal at high speed, thus achieving non-compression signal transmission even for high-vision video signals.
Optical wireless communications systems require optical-axis adjustments between an optical transmitter and an optical receiver. For example, Japanese Patent No. 3059870 discloses an optical-axis adjusting method which employs a guide (pilot) beam besides a light beam for signal transmission.
In usual all-in-one type TV sets having a video supply apparatus integrated with a video display apparatus, a user points a remote controller towards the video display apparatus for several adjustments to the video supply apparatus, such as, channel change and volume control.
Compared to all-in-one type TV sets, in separated-type video systems, such as the one illustrated in FIG. 2, a user must point a remote controller towards the video supply apparatus 1, not the video display apparatus 2, for adjustments to the video supply apparatus 1, such as, channel change and volume control.
Nevertheless, since most users are accustomed to point a remote controller towards a video display apparatus, he or she often cannot help but point a remote controller towards the video display apparatus 2, not the video supply apparatus 1, even in the video system illustrated in FIG. 2. This is very inconvenient for users.
In order to avoid such a problem, the video display apparatus 2 can be equipped with a control-signal receiver, a receiver for receiving a remote control signal sent from a remote controller.
The received remote control signal is transmitted from the optical receiver 5 to the video supply apparatus 1 via the optical transmitter 4.
Notwithstanding, such a system requires a control-signal transmitter at the optical receiver 5 while a control-signal receiver at the optical transmitter 4. This makes the system complex and expensive.
Moreover, in order to confirm whether the video display apparatus 2 and the optical receiver 5 are normally working, information on whether these apparatuses are normally working must be transmitted from the optical receiver 5 to the optical transmitter 4. This mechanism requires a transmitter for transmitting such information at the optical receiver 5 while a receiver for receiving such information at the optical transmitter 4. This also makes the system complex and expensive.